Smart tip: look to volume, not weight, for filtration media

Waterco Limited

By Alice Richard
Monday, 10 November, 2014

Smart tip: look to volume, not weight, for filtration media

When discussing the size of a filter, we tend to talk in terms of weight, rather than volume. But with different media types having different weights, is this really the most accurate way to size up a filter?

“One thing that we don’t talk often enough about is that we should always look at the volume, rather than just simply weight, because everything’s got different bulk densities,” said Waterco Marketing Director Bryan Goh.

“A lot of people ask, ‘How many kilos does this filter take?’ But if you just work by pure kilos, you’re looking at just the weight. Volume of filter media is what we are interested in - and volume is constant, whereas weights vary.

“Let’s say you get a 20-litre box and you fill it with 20 litres of water. That might weigh 20 kg. But if you get a 20-litre box and you fill it with lead weights, that could weigh 40 kg. But the volume is still the same: they’re both 20 litres.

“Filters are the same. They all have a set volume that you must achieve within the tank, but the weight is different depending on the filter media. Glass is more dense. Therefore, if I take a sand filter with a 50-litre volume and fill it with 50 litres of glass, it will weigh more than the sand did.

“If someone says, ‘That sand filter normally takes 100 kg of sand,’ and then they put in 100 kg of glass, they’ll have the wrong quantities. And it’s a pretty common mistake that’s made because, back in the day, before there was multiple filter media options, everyone just used sand.

“For instance, our Waterco 24″ filter takes 106 litres of media. That is 155 kg of sand. That is 171 kg of glass beads. And that is 127 kg of zeolite. Do you see my point?”

This can be an issue when changing a filter over from one media type to another, Goh says.

“If someone said, ‘That S660 [filter] takes 155 kg of media’ and they put in 155 kg of glass, then they’ve short-changed it - it should be 171 kg, so they’re missing 16 kg. But that volume is 106 litres, no matter what.

“In water treatment circles, you normally talk about the volume of a filter by litres, but in the pool industry, we always talk about [filter size] by weight. So we’ve got to be conscious of the kilograms-to-litres ratio to ensure we put the right amounts in.”

Image credit: ©

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